1. Field of the Invention
The present invention relates to systems for injecting chemicals, such as acid, into a subsea structure, such as a subsea tree. More particularly, the present invention relates to systems for injecting chemicals into a subsea structure in which the chemicals can be delivered by coiled tubing from a surface location. Additionally, the present invention relates to control systems used for the controlling of the operation of the subsea structure.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Over the recent past, the search for oil and gas in locations offshore has moved into progressively deeper water. Wells are now commonly drilled at depths of thousands of feet below the surface of the ocean. Additionally, wells are now being drilled in more remote offshore locations. The drilling and maintenance of deep and remote offshore wells is expensive. In an effort to reduce drilling and maintenance expenses, remote offshore wells are oftentimes drilled in clusters. A grouping of wells in a clustered subsea arrangement is sometimes referred to as a “subsea well site”. A subsea well site typically includes producing wells completed for production in at least one pay zone. In addition, a well site will often include one or more injection wells to aid in maintaining in-situ pressure for water drive and gas expansion drive reservoirs.
The grouping of subsea wells facilitates the gathering of production fluids into a local production manifold. Fluids from the clustered wells are delivered to the manifold by flowlines called “jumpers”. From the manifold, production fluids may be delivered together to a gathering and separating facility for a production line, or “riser”. For well sites that are in deeper waters, the gathering facility is typically a floating production storage and offloading vessel.
The clustering of wells also allows for multiple control lines and chemical treatment lines to extend from the ocean surface downwardly to the clustered wells. These lines are commonly bundled into one or more “umbilicals”. The umbilical terminates at an “umbilical termination assembly” at the ocean floor. A control line may carry hydraulic fluid used for controlling items of subsea equipment at subsea distribution units, manifolds and trees. Such control lines allow the actuation of safety valves and other subsea components from the surface. In addition, the umbilical may transmit chemical inhibitors to the ocean floor and then to equipment of the subsea processing system.
Often, a variety of chemicals (also referred to as “additives”) are introduced into the production wells and processing units to control, among other things, corrosion, scale, paraffin, emulsions, hydrates, hydrogen sulfide, asphaltens, inorganics and formation of other harmful chemicals. In offshore oilfields, a single offshore platform (e.g., a vessel, a semi-submersible, or a fixed system) can be used to supply these additives to several producing wells.
The equipment used to inject additives includes a chemical supply unit, a chemical injection unit, and a capillary or tubing (also referred to as a “conductor line”) that runs from the offshore platform through or along the riser and into the subsea well bore. Preferably, the additive injection system supply precise amounts of additives. It is also desirable for the systems to periodically or continuously monitor the actual amount of the additives being dispensed, determine the impact of the dispersed additives, and vary the amount of the additives as needed to maintain certain desired parameters of interest within their respectively desired ranges or at their desired values.
Coiled tubing has been increasingly used in the subsea environment. Coiled tubing can easily be placed upon large reels so that hundreds of feet of tubing can be easily deployed to the offshore location. In the past, coiled tubing has served a variety of purposes in delivering and removing fluids from the subsea environment. However, the coiled tubing has not seen great applicability in delivering and injecting chemicals into the subsea structure, such as a Christmas tree, or for the transmitting of control signals to the subsea tree. One of the problems associated with such coiled tubing is the possibility of damage created when extreme forces are applied to the tubing. Whenever the tubing would be disconnected by force from the subsea structure, damage to the subsea structure could occur and a resulting environmental event could also occur.
In the past, various patents have issued relating to injecting of fluids into subsea structures. For example, U.S. Pat. No. 5,085,277, issued on Feb. 4, 1992 to A. P. Hopper, describes a subsea well injection system in which a slurry of oil-impregnated cuttings from the use of the drilling mud are injected into the annulus of a subsea well and then into the porous formation through which the well has passed. This is accomplished using an apparatus on a guide base surrounding the subsea wellhead. The guide base includes a coupling for a pipe extending from the drilling rig, a one-way isolation valve and pipework leading to the outermost housing of the well. The outermost housing has ports to carry the slurry into the outermost annulus and inner housings also have ports to carry the slurry into the inner annuli. Interior housings also have a one-way check valve to control the injection.
U.S. Pat. No. 6,663,361, issued on Dec. 16, 2003 to Kohl et al., shows a subsea chemical injection pump for injecting chemicals into a subsea system at depths of up to 10,000 feet. This chemical injection pump employs an actuator, such as a solenoid, to power a double-acting actuator rod and plungers thereon. The pump generates low pressures and low fluid volumes.
U.S. Pat. No. 7,234,524, issued on Jun. 26, 2007 to Shaw et al., discloses a subsea chemical injection unit for additive injection and monitoring system for oilfield operations. The system monitors and controls the injection of additives into formations recovered through a subsea well. The system includes a chemical injection unit and a controller positioned at a remote subsea location. The injection unit utilizes a pump to supply one or more selected additives from a subsea or remote supply unit. The controller operates the pump to control the additive flow rates based on signals provided by sensors measuring a parameter of interest. The system includes a surface facility for supporting the chemical injection and monitoring activities.
U.S. Pat. No. 7,721,807, issued on May 25, 2010 to Stoisits et al., provides a method for managing hydrates in a subsea production line. The system has at least one producing well, a jumper for delivering produced fluids from the subsea well to a manifold, a production line for delivering produced fluids to a production gathering facility, and an umbilical for delivering chemicals to the manifold. The subsea well has been shut in so as to leave produced fluids in a substantially uninhibited state. The method generally comprises the steps of pumping a displacement fluid into the chemical injection tubing, pumping the displacement fluid through a chemical injection tubing provided in the umbilical, further pumping the displacement fluid through the manifold and into the production line, and pumping the displacement fluid through the production line so as to displace the produced fluids before hydrate formation may begin.
U.S. Pat. No. 8,133,041, issued a Mar. 13, 2012 to the Ludlow et al., provides a high-pressure pump for use in the injection of liquid chemicals into subsea oil and gas wells and adapted to be positioned in the subsea environment adjacent to the wellhead. The pump includes a piezoelectric actuator for reciprocating a plunger which acts to compress and expand the effect of volume of a pumping chamber. The pumping chamber has a valved inlet connected to a source of liquid and a valved outlet to lead the liquid to the well.
U.S. Pat. No. 8,430,169, issued on Apr. 30, 2013 to Stoists et al., provides a method for managing hydrates in a subsea line. The production system includes a host production facility, a controlled umbilical, at least one subsea production well, and a single production line. The method includes the steps of depressurizing the production line to substantially reduce a solution gas concentration in the produced hydrocarbon fluids, and then re-pressurizing the production line to urge any remaining gas in the free gas phase within the production line back into solution.
U.S. Pat. No. 8,555,914, issued on Oct. 15, 2013 to Smith et al., discloses a method for autonomous control of chemical injection systems for oil and gas wells. A control program for a positive displacement metering system measures the time required for the travel of a free piston in a cylinder of known volume to determine an average flow rate during a full stroke of the piston. The system also measures and records the inlet and outlet pressures between the fluid inlet and the outlet. The control program positions a four-way valve which may function as an adjustable metering orifice in response to the measured average flow rate and/or changes in the inlet and outlet pressures to achieve the desired flow rate. At the end of each stroke, the four-way valve is repositioned to reverse fluid flow through the metering cylinder.
U.S. Patent Publication No. 2014/0318797, published on Oct. 30, 2014 to Vangasse et al., describes a method of applying an acid wash to a subsea connection assembly in order to remove unwanted material such as marine growth and calcareous deposits. The method includes inserting a plug containing channels into a central hole in a stabplate connection. The acid wash is then injected through the plug. The plug may be carried by an operating tool arm of a remotely operated underwater vehicle.
It is an object of the present invention to facilitate the delivery of electrical power and communications to a subsea structure, such as a subsea tree.
It is another object of the present invention to provide a subsea chemical injection system that minimizes the likelihood of environmental impacts.
It is another object the present invention to provide a subsea chemical injection system that minimizes the possibility of damage to subsea hardware.
It is another object of the present invention to provide a subsea chemical injection system that facilitates emergency shutdown.
It is still a further object of the present invention to provide a subsea chemical injection system that can be easily installed and which utilizes coiled tubing.
It is another object of the present invention to provide a subsea chemical injection system which minimizes the potential for the introduction of fatigue loads to the coiled tubing and manifold assembly.
It is still further object of the present invention divided provide a subsea chemical injection system that can increase the vessel operating parameters in comparison with rigid connections.
It is another object of the present invention to provide a subsea chemical injection system which provides a conduit for the purpose of transmitting subsea chemicals and electrical signals.
It is still another object of the present invention to provide a subsea chemical injection system that facilitates the injection of chemicals into the subsea tree from a surface vessel.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.